Many types of scientific monitors utilize a tape or piece of paper to record or gather the monitored information. For example, in a remote working level meter, such as described in U.S. Pat. No. 3,555,278 of Schroeder entitled "Potential Alpha Ray Activity Meter," a test sample is collected by exposing a portion of porous tape to a volume of air. Detection means are then utilized to determine from the tape whether particular elements are present. Manual handling, in such a device, may be minimized by providing it with a tape transport mechanism. In such devices, the exposure of the tape, normally a porous filter paper, is done by pumping a known flow rate of air through a fixed area of the tape for a fixed time period at one station and then transporting the tape with the tape transport mechanism to another station where detection is undertaken. The transport mechanism handles a supply of tape so that a plurality of monitoring events can be obtained without the necessity of continually changing the tape for each monitoring event.
To insure the proper accuracy of the measurements obtained from such a portable monitor, it is necessary that the transporting of the tape between stations be in a precise manner so that the entire area of the tape that has collected the desired sample is repeatedly positioned in a precise geometry with respect to the detector. Prior art stepwise tape transport mechanisms include tape perforated at precise intervals with the intervals detected such as by a photoelectric cell. For certain types of tough plastic tape, perforating is difficult. Another stepwise transport mechanism is an indexed takeup reel which takes up a precise interval of tape. An indexed takeup reel, however, has a higher degree of inaccuracy than may be desirable.
It is therefore an object of this invention to provide a mechanism for transporting a tape between two or more stations.
Another object of this invention is to provide such a tape transport mechanism wherein movement of the tape is in a precise stepwise fashion.